U.S. patent application number 15/103805 was filed with the patent office on 2016-11-10 for cleaning of liquid hydrocarbon streams by means of copper-containing sorbents.
The applicant listed for this patent is EVONIK DEGUSSA GMBH. Invention is credited to Frank Geilen, Dietrich Maschmeyer, Stephan Peitz, Armin Rix, Guido Stochniol, Mathias Vogt, Markus Winterberg.
Application Number | 20160326442 15/103805 |
Document ID | / |
Family ID | 51862313 |
Filed Date | 2016-11-10 |
United States Patent
Application |
20160326442 |
Kind Code |
A1 |
Geilen; Frank ; et
al. |
November 10, 2016 |
CLEANING OF LIQUID HYDROCARBON STREAMS BY MEANS OF
COPPER-CONTAINING SORBENTS
Abstract
The invention relates to a method for cleaning hydrocarbon
mixtures, in which a contaminated hydrocarbon mixture comprising
hydrocarbons having three to eight carbon atoms is at least partly
freed of impurities by contacting with a solid sorbent, wherein the
hydrocarbon mixture is exclusively in the liquid state during
contact with the sorbent. The object of the invention is to specify
a process for cleaning liquid C.sub.3 to C.sub.8 hydrocarbon
mixtures, which is based on a readily available but
non-carcinogenic sorbent and which achieves better purities
compared to traditional molecular sieves. This object is achieved
by using, as sorbents, solid materials of the following
composition: copper oxide: 10% to 60% by weight (calculated as
CuO); zinc oxide: 10% to 60% by weight (calculated as ZnO);
aluminum oxide: 10% to 30% by weight (calculated as
Al.sub.2O.sub.3); other substances: 0% to 5% by weight. Materials
of this kind are otherwise used as catalysts in methanol
synthesis.
Inventors: |
Geilen; Frank; (Haltern am
See, DE) ; Peitz; Stephan; (Oer-Erkenschwick, DE)
; Stochniol; Guido; (Haltern am See, DE) ;
Winterberg; Markus; (Waltrop, DE) ; Maschmeyer;
Dietrich; (Recklinghausen, DE) ; Rix; Armin;
(Marl, DE) ; Vogt; Mathias; (Essen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EVONIK DEGUSSA GMBH |
Essen |
|
DE |
|
|
Family ID: |
51862313 |
Appl. No.: |
15/103805 |
Filed: |
November 5, 2014 |
PCT Filed: |
November 5, 2014 |
PCT NO: |
PCT/EP2014/073763 |
371 Date: |
June 10, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 20/08 20130101;
B01J 20/2803 20130101; B01J 20/06 20130101; B01J 23/80 20130101;
B01J 35/0053 20130101; C10G 25/003 20130101; C10G 57/02 20130101;
C07C 7/13 20130101; C10G 25/05 20130101; C10G 53/14 20130101; C10G
57/00 20130101; B01J 2220/42 20130101; C10G 55/04 20130101; C10G
67/06 20130101; C10G 53/08 20130101; C10G 57/005 20130101; C10G
2300/202 20130101; C07C 11/08 20130101; C07C 7/13 20130101 |
International
Class: |
C10G 25/00 20060101
C10G025/00; C10G 57/02 20060101 C10G057/02; B01J 20/08 20060101
B01J020/08; C10G 53/14 20060101 C10G053/14; C10G 53/08 20060101
C10G053/08; C10G 67/06 20060101 C10G067/06; C10G 57/00 20060101
C10G057/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2013 |
DE |
10 2013 225 724.4 |
Claims
1. Process for purifying hydrocarbon mixtures, in which a
contaminated hydrocarbon mixture comprising hydrocarbons having
three to eight carbon atoms is at least partly freed of
contaminants by contacting it with a solid sorbent, the hydrocarbon
mixture being exclusively in the liquid state during the contact
with the sorbent, wherein the sorbent has the following composition
that adds up to 100% by weight: copper oxide: 10% to 60% by weight
(calculated as CuO); zinc oxide: 10% to 60% by weight (calculated
as ZnO); aluminium oxide: 10% to 30% by weight (calculated as
Al.sub.2O.sub.3); other substances: 0% to 5% by weight.
2. Process according to claim 1, wherein the sorbent has the
following composition that adds up to 100% by weight: copper oxide:
30% to 45% by weight (calculated as CuO); zinc oxide: 30% to 50% by
weight (calculated as ZnO); aluminium oxide: 10% to 15% by weight
(calculated as Al.sub.2O.sub.3); further metal oxides: 0% to 2% by
weight; graphite: 0% to 3% by weight; other substances: 0% to 1% by
weight.
3. Method according to claim 1, whereby the contact is effected in
the absence of hydrogen.
4. Method according to claim 1, whereby the contact is effected
under the following conditions: temperature between 10.degree. C.
and 150.degree. C., especially between 20.degree. C. and
130.degree. C. and more preferably between 30.degree. C. and
120.degree. C.; pressure between 0.5 and 3.5 MPa; space-time yield
(weight hourly space velocity--WHSV) between 0.5 h.sup.-1 and 7
h.sup.-1.
5. Process according to claim 1, wherein the contaminated
hydrocarbon mixture contains at least one impurity from one of the
following substance classes: a) thiols having the general formula
R--SH where R may be an alkyl, aryl, cycloalkyl or alkenyl radical,
where R is especially a methyl, ethyl, propyl, butyl, phenyl,
cyclohexyl or butenyl radical; b) disulphides having the general
formula R--S--S--R' where R and R' may be identical or different
alkyl, aryl, cycloalkyl or alkenyl radicals, where R and R' are
especially methyl, ethyl, propyl, butyl, phenyl, cyclohexyl or
butenyl radicals; c) sulphides having the general formula R--S--R'
where R and R' may be identical or different alkyl, aryl,
cycloalkyl or alkenyl radicals, where R and R' are especially
methyl, ethyl, propyl, butyl, phenyl, cyclohexyl or butenyl
radicals; d) substituted or unsubstituted sulphur-containing
heterocycles, especially thiophenes and/or thiolanes.
6. Process according to claim 1, wherein the proportion by weight
of the contaminants in the contaminated hydrocarbon mixture, based
on the total weight thereof, is less than 0.2% by weight, more
preferably below 100 ppm by weight and most preferably below 10 ppm
by weight.
7. Process according to claim 1, wherein the contaminated
hydrocarbon mixture is obtained from a pre-purification stage which
pre-purifies a more highly contaminated raw material mixture to
obtain the contaminated hydrocarbon mixture.
8. Process according to claim 7, wherein the sorbent is used
irreversibly.
9. Process according to claim 1, wherein the contaminated
hydrocarbon mixture fulfils one of the following specifications A,
B, C and D, each of which adds up to 100% by weight, the stated
proportions by weight each being based on the total weight of the
contaminated hydrocarbon mixture: Specification A: isobutane 20% to
40% by weight, preferably 30% to 37% by weight; n-butane 5% to 18%
by weight, preferably 8% to 10% by weight; 1-butene 5% to 15% by
weight, preferably 12% to 14% by weight; isobutene 12% to 25% by
weight, preferably 15% to 20% by weight; 2-butenes 9% to 40% by
weight, preferably 20% to 30% by weight; 1,3-butadiene 0% to 3% by
weight, preferably 0.5% to 0.8% by weight; water 0% to 1% by
weight, preferably less than 0.1% by weight; contaminants,
especially sulphur-containing hydrocarbons, less than 0.5% by
weight, preferably less than 0.2% by weight; Specification B:
isobutane 0.6% to 8% by weight, preferably 1% to 7% by weight;
n-butane 0.5% to 8% by weight, preferably 4% to 7% by weight;
1-butene 9% to 25% by weight, preferably 10% to 20% by weight;
isobutene 10% to 35% by weight, preferably 20% to 30% by weight;
2-butenes 3% to 15% by weight, preferably 5% to 10% by weight;
1,3-butadiene 25% to 70% by weight, preferably 40% to 50% by
weight; water 0% to 1% by weight, preferably less than 0.5% by
weight; contaminants, especially sulphur-containing hydrocarbons,
less than 0.5% by weight, preferably less than 0.2% by weight;
Specification C: isobutane 0.6% to 8% by weight, preferably 1% to
7% by weight; n-butane 0.5% to 15% by weight, preferably 4% to 13%
by weight; 1-butene 9% to 40% by weight, preferably 10% to 35% by
weight; isobutene 10% to 55% by weight, preferably 20% to 50% by
weight; 2-butenes 3% to 25% by weight, preferably 5% to 20% by
weight; 1,3-butadiene 0% to 1% by weight, preferably less than 0.8%
by weight; water 0% to 1% by weight, preferably less than 0.5% by
weight; contaminants, especially sulphur-containing hydrocarbons,
less than 0.5% by weight, preferably less than 0.2% by weight;
Specification D: n-butane 10% to 30% by weight, preferably 25% to
30% by weight; 1-butene 0.2% to 45% by weight, preferably 5% to 30%
by weight; 2-butenes 35% to 85% by weight, preferably 50% to 75% by
weight; water 0% to 1% by weight, preferably less than 0.1% by
weight; contaminants, especially sulphur-containing hydrocarbons,
less than 0.5% by weight, preferably less than 0.1% by weight.
10. Process according to claim 1, wherein the hydrocarbon mixture
which has been at least partly freed of contaminants is subjected
to at least one of the workup steps enumerated below: a) extraction
of 1,3-butadiene present in the hydrocarbon mixture; b) selective
hydrogenation of diolefins and/or acetylenes present in the
hydrocarbon mixture to olefins; c) oligomerization of olefins
present in the hydrocarbon mixture to corresponding oligomers; d)
distillative removal of 1-butene and/or isobutane present in the
hydrocarbon mixture, especially with the purpose of obtaining
1-butene and/or isobutane in high purity; e) removal of isobutene
present in the hydrocarbon mixture by conversion of the isobutene
with water to tert-butanol and/or with methanol to methyl
tert-butyl ether; f) dehydrogenation of butanes present in the
hydrocarbon mixture to butenes; g) oxidative dehydrogenation of
butenes present in the hydrocarbon mixture to butadiene; h)
alkylation of n-butene present in the hydrocarbon mixture with
isobutane likewise present; i) oxidation of hydrocarbons having
four carbon atoms present in the hydrocarbon mixture for
preparation of maleic anhydride.
11. (canceled)
Description
[0001] The invention relates to a process for purifying hydrocarbon
mixtures, in which a contaminated hydrocarbon mixture comprising
hydrocarbons having three to eight carbon atoms is at least partly
freed of contaminants by contacting it with a solid sorbent, the
hydrocarbon mixture being exclusively in the liquid state during
the contact with the sorbent.
[0002] Hydrocarbons are compounds consisting exclusively of carbon
and hydrogen. The nomenclature of the hydrocarbons is based on the
number of carbon atoms present per molecule of the hydrocarbon. In
abbreviated notation, the prefix C.sub.n is commonly used, where n
is said number.
[0003] C.sub.4 hydrocarbons are consequently compounds consisting
exclusively of carbon and hydrogen, where the number of carbon
atoms per molecule is four. Important representatives of the
C.sub.4 hydrocarbons are the alkenes and alkanes having four carbon
atoms.
[0004] Mixtures of C.sub.4 hydrocarbons are raw materials from
downstream petrochemistry. They originate, for example, from
steamcrackers (so-called "crack C4"), from catalytic crackers
(so-called "FCC C4" (FCC: "fluid catalytic cracking") or "DCC C4"
(DCC: "deep catalytic cracking"), from pyrolysis ("pyrolysis C4"),
from MTO or MTP processes (MTO: "methanol to olefins", MTP:
methanol to propylene) or dehydrogenations of isobutane and
n-butane. The most common are C.sub.4 hydrocarbons from
steamcrackers (crack C4) and from catalytic crackers (FCC C4).
Mixtures of C.sub.4 mixtures of different origin are also traded,
called "C.sub.4 cut". For the purpose of utilizing the individual
components, the C.sub.4 mixtures have to be divided into their
constituents with maximum purity.
[0005] The workup of C.sub.4 streams from steamcrackers or
catalytic crackers is described in principle in K.-D. Wiese, F.
Nierlich, DGMK-Tagungsbericht [German Society for Petroleum and
Coal Science and Technology, Conference Report] 2004-3, ISBN
3-936418-23-3. A comprehensive overall process description can be
found in DE102008007081A1.
[0006] The aspects of C.sub.4 workup that are relevant to this
invention are outlined briefly hereinafter.
[0007] Technical C.sub.4 hydrocarbon mixtures from the
above-described sources typically contain not only saturated and
monounsaturated compounds but also polyunsaturated compounds.
Before individual compounds can be isolated from these mixtures, it
is frequently necessary to remove other compounds to the maximum
possible degree. This can be effected by physical methods, for
example distillation, extractive distillation or extraction, but
also by a selective chemical conversion of the components to be
removed. Particular attention has to be paid to the maximum
possible removal of the contaminants such as oxygen-, nitrogen- and
sulphur-containing components present in the C.sub.4 hydrocarbon
mixture, since these can have adverse effects on the individual
process steps as catalyst poisons. While these impurities are
typically present only in traces in crack C4, they may also be
present in higher concentrations, for example, in FCC C4
streams.
[0008] C.sub.4 hydrocarbon mixtures from steamcrackers or fluidized
catalytic crackers typically have the main components listed in
Table 0 (contaminants not shown).
TABLE-US-00001 TABLE 0 Typical compositions of crack C4 and FCC C4
Crack C4 FCC C4 Component [% by wt.] [% by wt.] isobutane 1-3 20-40
n-butane 6-11 5-15 1-butene 14-20 10-20 2-butenes 4-8 20-35
isobutene 20-28 10-20 1,3-butadiene 40-45 less than 1
[0009] The composition of the raw materials may vary significantly
according to the origin of the material. The C.sub.4 components
listed are supplemented by hydrocarbons having fewer or more carbon
atoms, and contaminants such as mercaptans, sulphides, disulphides,
nitrogen- and oxygen-containing compounds in small amounts.
[0010] In one variant, the workup of FCC C4 can be effected in such
a way that the concentration of isobutane is first lowered by means
of a distillative step in a distillation to a value of less than 5%
by weight, more preferably less than 3% by weight. At the same
time, the low boilers present in the mixture (for example C.sub.3
hydrocarbons, light oxygen-, nitrogen- and sulphur-containing
compounds) are removed or minimized. In the subsequent step, in a
column, all the high boilers (for example C.sub.5 hydrocarbons,
heavy oxygen-, nitrogen- and sulphur-containing compounds) are
removed via the bottom. In the next step, isobutene is removed, for
example by reacting it with methanol to give methyl tert-butyl
ether (MTBE), and the latter is removed by distillation. If pure
isobutene is to be obtained, the methyl tert-butyl ether is
subsequently cleaved again to isobutene and methanol.
[0011] For further workup of the C.sub.4 mixture, the
polyunsaturated compounds still remaining have to be converted with
the aid of a selective hydrogenation process to the corresponding
monounsaturated and saturated compounds. Now 1-butene and remaining
isobutane can be removed by distillation in sufficient purity, and
the remaining 2-butenes and the n-butane can be subjected to
further workup. Frequently, the 2-butenes are converted by
oligomerization, more specifically by dimerization to octenes. This
forms one molecule having eight carbon atoms from two molecules
each having four carbon atoms. The octenes can subsequently be
converted by means of hydroformylation to PVC plasticizer alcohols.
The saturated C4 hydrocarbons that remain after the olefins have
been depleted can especially be used as propellants for
aerosols.
[0012] An oligomerization is understood to mean a process in which
higher alkenes having 6-20 carbon atoms are formed from olefins,
such as, more particularly, from propene and butenes. An example of
a process employed industrially is the nickel-catalysed OCTOL.RTM.
process, which is described in detail in Hydrocarbon Process., Int.
Ed. (1986) 65 (2. Sect. 1), pages 31 to 33, and in DE3914817,
EP1029839 and DE102004018753.
[0013] The input streams used for the individual process steps have
generally already attained a high degree of purity through
preceding processes in which impurities were removed again and
again. However, remaining impurities can reversibly or even
irreversibly deactivate the catalyst. This deactivation should of
course be reduced to a minimum for economic reasons. Therefore, as
many catalyst poisons as possible should be kept away from the
catalyst by further purification stages.
[0014] The various catalyst poisons present in the technical
C.sub.4 mixtures have poisoning effects in different ways. For
instance, the acidic catalyst systems or system components such as
cocatalysts are poisoned almost exclusively by components which are
themselves basic or at least release bases as a result of further
reactions. A particularly typical example of such substances is
acetonitrile which, as a very weak base, is comparatively difficult
to remove by sorption processes. However, it reversibly poisons
strong Lewis acids. In the presence of traces of water, it is
hydrolysed via acetamide to the strong base ammonia, which then
irreversibly deactivates Bronsted acids as well through formation
of ammonium ions. Incidentally, even water itself is always a
partial catalyst poison, but the effect thereof is generally
reversible, provided that it does not contribute to the formation
of stronger catalyst poisons through further reactions. For the
nickel-catalysed oligomerization of butenes over the OCTOL.RTM.
catalyst, even a water content of about 5 ppm leads to measurable
deactivation. However, the water is added onto olefins by many
systems, and the alcohols formed are oxidized by the standard
catalyst systems via a transfer hydrogenation, with hydrogenation
of other unsaturated components, until thermodynamic equilibrium
has been attained.
[0015] The metal complex catalysts too are sensitive to basic
substances. The poisoning effect is usually manifested primarily
via the deactivation of the acidic cocatalyst.
[0016] The metal component of the catalysts, in contrast, is
attacked particularly strongly by components such as sulphur in the
form of particular compounds, and this under particular
circumstances irreversibly destroys the metal hydride or metal
complex through formation of sparingly soluble sulphides. Since the
metals are generally in very low oxidation states, sulphur
compounds that are able to oxidize the metals to a relatively high
oxidation state, for example di- and polysulphides, are
particularly effective. Different sulphur compounds are thus able
to have quite different primary effects. While, for example,
disulphides react extremely efficiently to give thioethers and
sulphur, which then oxidizes the metal hydrides to form sulphides,
the primary effect of thioethers themselves at first is probably
solely as a Lewis base. Through further processes and reactions,
which are generally not even known in detail, with further trace
components in the system, however, they also lead
ultimately--albeit much more slowly--to the formation of metal
sulphides as well.
[0017] According to the above statements, for maximum economic
viability of operation of a plant for fractionation of hydrocarbon
mixtures into their constituents of value with the aid of catalytic
reaction units, the problem is thus to protect catalysts with
maximum efficacy from catalyst poisons and especially sulphur
compounds. The more reactant the catalyst is to specifically
convert, the more strongly this applies, and so this applies
particularly to heterogeneous catalysts such as those of the
OCTOL.RTM. process.
[0018] Sulphur-containing poisons are generally removed by an
alkaline scrub in the propene and butene streams in question. In
this scrub, hydrogen sulphide and mercaptans react particularly
efficiently. In general, the alkaline scrubbing solutions are
regenerated by oxidation with air.
[0019] Such a scrubbing process is offered for industrial use by
UOP LLC under the MEROX.RTM. name (G. A. Dziabis, "UOP MEROX
PROCESS" in Robert Meyers, Handbook of Petroleum Refining
Processes, 3rd Edition, 2004 McGraw-Hill).
[0020] In the MEROX.RTM. process, the mercaptans are oxidized in
the aqueous scrubbing solution to di- and polysulphides, which are
removed as oily phase. However, a small portion of these di- and
polysulphides remains dissolved or suspended in the aqueous alkali
metal hydroxide solution, and it is often not possible even by
scrubbing this aqueous phase with a scrubbing oil or the like to
quantitatively remove this residue before recycling into the
scrubbing, such that the mercaptans are substantially removed but,
on the other hand, small amounts of di- and polysulphides are
introduced back into the stream. As just mentioned, these are
sulphur components which convert the metal hydrides that are
essential to the reaction to sparingly soluble metal sulphides and
hence irreversibly deactivate the catalyst. Typically, for example,
the streams of FCC C4 contain about 100 to 200 ppm of sulphur.
After the MEROX.RTM. scrub, this content has then typically been
reduced to a value below 10 ppm, and the sulphur compounds then
consist predominantly of the di- and polysulphides mentioned, but
also of higher mercaptans.
[0021] In practice, a portion of the poisons, through skilful
arrangement of separating operations, for example distillations,
can also be directed into fractions in which they no longer come
into contact with sensitive catalysts. Frequently, however, this is
not possible to the extent that seems desirable with regard to the
purity of the streams, such that sorbents have to be inserted
upstream of the catalyst beds, in order to assure the required
purity.
[0022] Sorbents are solid substances that are capable of binding
another substance, called the sorbate, if they come into contact
with the sorbate. The binding is effected at the surface of the
sorbent through physical and/or chemical effects. In this respect,
a distinction is made between physical and chemical adsorption.
Since the mode of action of a sorbent is not always unambiguously
clear, reference is made here to a sorbent, without attributing the
effect.
[0023] From a technical point of view, sorbents should generally be
distinguished into those which are regeneratable and those that
irreversibly convert or chemically bind the catalyst poisons.
[0024] Regeneratable sorbents used are frequently molecular sieves
and zeolites. Regeneratable sorbents bind soiling materials only
with moderate strength. In the course of regeneration of the
sorbent, conditions such as higher temperatures and lower
pressures, for example, under which the sorbent releases the
sorbate again, are established. These properties lead to a
relatively low capacity before breakthrough. In addition, high
operating costs often arise through discharge and flushing of the
sorbent and through the provision and disposal of the regenerating
gases or else of the liquid streams.
[0025] Irreversible sorbents, in contrast, are not regenerated but
disposed of after breakthrough. They therefore have to be available
and disposable inexpensively. Since irreversible sorbents
chemically bind the adsorbate, the permeability thereof with
respect to the substances to be absorbed is lower than in the case
of regeneratable sorbents. Irreversible sorbents therefore achieve
better purity levels than regeneratable sorbents.
[0026] EP 0 064 464 A1 describes catalyst materials usable
particularly for desulphurization of hydrocarbon batches. The
catalyst materials contain copper oxide and are based on a support
composed of alumina or type X or Y zeolite. A matter of concern is
the obligatory content of cadmium oxide, since cadmium is
classified as carcinogenic. Carcinogenic substances can be handled
and disposed of only with high cost and inconvenience, and so
particularly the irreversible use of such catalyst materials is
uneconomic.
[0027] EP 0 354 316 B1 describes the cadmium-free fine
desulphurization of liquid C.sub.4 hydrocarbon mixtures over
zeolites containing copper, silver and zinc. The preferred
temperature range is between 50 and 130.degree. C., the preferred
pressure 1 to 50 bar. The weight hourly space velocity is reported
as 1 to 40 h.sup.-1. Even though the sorbent described here does
not contain any potentially hazardous cadmium, this material is
likewise uneconomic because of its high silver content of at least
2% by weight.
[0028] Nickel-containing oligomerization catalysts are particularly
prone to catalyst poisons. Hydrocarbon mixtures having two to four
carbon atoms often serve as substrate for oligomerizations such as
the OCTOL.RTM. process. In order to effectively remove catalyst
poisons, it has been found to be useful to pass such streams over a
molecular sieve before entry into the oligomerization. For
instance, EP0395857B1 describes a process of this type, in which a
desulphurization of refinery propene, prior to oligomerization
thereof, is effected over a copper-exchanged X zeolite at a
temperature of 120.degree. C., a pressure of 50 bar abs. and a
weight hourly space velocity of 0.75 h.sup.-1. Under these
conditions, propene is supercritical.
[0029] Since these simple molecular sieves are readily available
and do not present any potential hazard to health, they are
nowadays the sorbents of choice in industrial practice for fine
desulphurization of C.sub.3 to C.sub.8 hydrocarbon mixtures. Since
the molecular sieves bind the contaminants only by physical means,
sorbents of this kind can be regenerated. However, the sorption
capacity thereof is lower compared to chemical sorbents, such that
only moderate purities are achievable by fine desulphurization over
zeolites.
[0030] With respect to this prior art, the problem addressed by the
invention is that of specifying a process for purifying liquid
C.sub.3 to C.sub.8 hydrocarbon mixtures, which is based on a
readily available but non-carcinogenic sorbent and which achieves
better purity levels compared to conventional molecular sieves.
[0031] At the same time, the process should also have the following
properties: [0032] the sorbent used should have a maximum binding
capacity for sulphur compounds and remove them substantially
completely from the contaminated hydrocarbon mixture; [0033] the
process should incur low operating costs; more particularly, it
should be operable without the permanent supply of additional
operating materials, for example hydrogen; [0034] the sorbent
should be usable "out of the box" without any pretreatment, such as
a hydrogenation or oxidation; [0035] it should be possible to
handle the sorbent without risk; more particularly, it should not
exhibit any pyrophoric properties; [0036] there should be no loss
of olefinic materials of value over the sorbent through side
reactions such as oligomerization, isomerization or
hydrogenation.
[0037] This problem is surprisingly solved by using, as the
sorbent, solid materials of the following composition: [0038]
copper oxide: 10% to 60% by weight (calculated as CuO); [0039] zinc
oxide: 10% to 60% by weight (calculated as ZnO); [0040] aluminium
oxide: 10% to 30% by weight (calculated as Al.sub.2O.sub.3); [0041]
other substances: 0% to 5% by weight.
[0042] The invention therefore provides a process for purifying
hydrocarbon mixtures, in which a contaminated hydrocarbon mixture
exclusively in the liquid state, comprising hydrocarbons having
three to eight carbon atoms, is at least partly freed of
contaminants by contacting it with a solid sorbent of the following
composition that adds up to 100% by weight: [0043] copper oxide:
10% to 60% by weight (calculated as CuO); [0044] zinc oxide: 10% to
60% by weight (calculated as ZnO); [0045] aluminium oxide: 10% to
30% by weight (calculated as Al.sub.2O.sub.3); [0046] other
substances: 0% to 5% by weight.
[0047] The sorbents used in accordance with the invention are
commercially available in a simple manner, namely as catalysts for
methanol synthesis:
[0048] In the field of methanol synthesis, copper/zinc/aluminium
catalysts have been found to be useful in industry. Methanol is
synthesized from carbon monoxide and hydrogen, or as a side
reaction from carbon dioxide and hydrogen, which additionally gives
water. Both reactions are thus conducted in the presence of the
reactant hydrogen. When copper/zinc/aluminium catalysts are used,
the methanol synthesis is conducted at temperatures between
220.degree. C. and 230.degree. C. and a pressure of about 5 MPa (50
bar). Under these conditions, the reactants and products are in the
gas phase.
[0049] Copper/zinc/aluminium catalysts for methanol synthesis have
been described many times in the patent literature:
[0050] For instance, DE2846614C3 discloses a process for preparing
methanol from a gas mixture of CO, CO.sub.2 and H.sub.2 at
temperatures of 200 to 350.degree. C. in the presence of a catalyst
containing 38.3% Cu, 48.8% Zn and 12.9% Al.
[0051] DE1568864C3 points out that synthesis gas should be
desulphurized for methanol production, since copper catalysts can
easily be poisoned with sulphur. The copper/zinc/aluminium catalyst
described here contains more than 35% by weight of copper; the zinc
content is 15% to 50% by weight. The aluminium content is reported
as 4% to 20% by weight.
[0052] EP0125689B2 describes a catalyst for methanol synthesis,
which comprises copper oxide and zinc oxide as catalytically active
substances, and also--as a thermally stabilizing
substance--aluminium oxide. In the unreduced state, catalyst
precursors produced by way of example have, for instance, 65% to
68% by weight of CuO, 21% to 23% by weight of ZnO and 10% to 12% by
weight of Al.sub.2O.sub.3. The specific surface area is 100 to 130
g/m.sup.2. The methanol synthesis is effected at 250.degree. C. and
50 bar.
[0053] Similar methanol catalysts having 63% to 65% by weight of
CuO, 24% to 27% by weight of ZnO and 10% to 11% by weight of
Al.sub.2O.sub.3 are described in DE10160486A1.
[0054] A catalyst having a comparatively low copper content and
high zinc content (43.2% by weight of CuO, 47.0% by weight of ZnO
and 10.2% by weight of Al.sub.2O.sub.3) was produced in U.S. Pat.
No. 4,279,781. However, the catalytic activity thereof in methanol
synthesis was rated as comparatively poor.
[0055] Because of the great industrial significance of the
synthesis of methanol, a commodity chemical, copper/zinc/aluminium
catalysts have not just been described in theoretical terms in the
patent literature but are also readily commercially available. The
disposal thereof is comparatively unproblematic, since no
carcinogenic substances are present. Incidentally, the recycling of
such sorbents is economically attractive, since this material
contains a large amount of valuable copper.
[0056] The invention is based partly on the finding that
commercially available methanol catalysts are suitable for
purification of typical raw material streams in downstream
petrochemistry. This is because it has been found that catalysts of
this kind, when they are contacted with liquid hydrocarbon mixtures
as sorbents, react well with the sulphur compounds even without
supply of hydrogen. They react particularly quickly with
mercaptans.
[0057] The invention therefore also provides for the use of a solid
having the following composition: [0058] copper oxide: 10% to 60%
by weight (calculated as CuO); [0059] zinc oxide: 10% to 60% by
weight (calculated as ZnO); [0060] aluminium oxide: 10% to 30% by
weight (calculated as Al.sub.2O.sub.3); [0061] other substances: 0%
to 5% by weight for purification of liquid hydrocarbon mixtures
comprising hydrocarbons having three to eight carbon atoms.
[0062] The usability of methanol catalysts based on
CuO/ZnO/Al.sub.2O.sub.3 that has been recognized in accordance with
the invention for removal of poisons from hydrocarbon mixtures is
surprising because the methanol synthesis is always effected in the
presence of hydrogen, whereas hydrogen is generally not present to
a significant degree in the streams from which poisons are to be
removed. Thus, crack C4 and FCC C4 streams that are customary on
the market are free of hydrogen (<1 ppm by weight). The removal
of poisons from such streams is thus effectively effected in the
absence of hydrogen.
[0063] Furthermore, the workup of C.sub.3 to C.sub.8 hydrocarbon
mixtures is generally effected in the liquid phase, since the
hydrocarbons having more than two carbon atoms are liquefied with a
low level of expenditure and can then be processed with a high
process intensity. However, methanol synthesis is effected
exclusively in the gas phase. It was not to be expected that
materials intended for gas phase catalysis would also be suitable
for liquid phase sorption.
[0064] In principle, any commercially available Cu/Zn/Al catalyst
is suitable as a sorbent for purification of the C.sub.3 to C.sub.8
hydrocarbon mixtures. However, preference is given to using those
catalysts which have the following composition: [0065] copper
oxide: 30% to 45% by weight (calculated as CuO); [0066] zinc oxide:
30% to 50% by weight (calculated as ZnO); [0067] aluminium oxide:
10% to 15% by weight (calculated as Al.sub.2O.sub.3); [0068]
further metal oxides: 0% to 2% by weight; [0069] graphite: 0% to 3%
by weight; [0070] other substances: 0% to 1% by weight.
[0071] Useful further metal oxides in this context are, for
example, iron oxides or magnesium oxides. Heavy metal oxides, which
are known to be hazardous to health, for example cadmium or lead or
chromium, should not be present if possible. Small amounts of
graphite or magnesium stearate serve as binders for better shaping
of the sorbent. "Other substances" in this context are understood
to mean production-related contaminants of the sorbent.
[0072] With regard to the shaping, the sorbent may be present in
powder form or in the form of granules. In addition, the sorbent
can be pressed into a macroscopic form, for example into spheres,
or into pellets or into rings.
[0073] Suitable methods for the production of the sorbent are in
principle all the technical methods that lead to a solid having
sufficient stability for handling. It encompasses essentially the
two steps of: [0074] y) providing a porous framework material
composed of aluminium oxide and/or graphite; [0075] z) blending the
framework material with copper oxide and zinc oxide.
[0076] It is possible to use copper oxide powder, copper carbonate
powder or hydroxide-containing copper compounds, and mixtures
thereof. In the case of copper, it is also possible to convert a
copper carbonate-containing compound, with the aid of an ammoniacal
solution, fully or partly to a copper tetraammine carbonate
solution which serves as starting material. These substances are
mixed, in accordance with the inventive mixing ratios, together
with zinc oxide, zinc carbonate or zinc hydroxide and an
Al.sub.2O.sub.3-containing powder. Instead of Al.sub.2O.sub.3, it
is also possible to partly use SiO.sub.2. As
Al.sub.2O.sub.3-containing powder, it is possible to use all the
polymorphs of Al.sub.2O.sub.3, and also aluminium oxide hydrate or
aluminium hydroxy oxides and aluminium hydroxide. The individual
solid components can be blended and homogenized in suitable mixers,
intensive mixers or kneaders. In this process, it is customary to
undertake moistening with demineralized water. Adequate mixing may
be followed by any suitable shaping operation. Under some
circumstances, complete or partial drying and/or grinding of the
mixture is necessary beforehand. For the shaping, extruders or
tableting presses, for example, are suitable. Pan pelletizers may
be appropriate for these purposes. In the case of tableting, a
lubrication aid such as graphite is often added to the mixture. In
the case of extrusion, other organic additives suitable for
establishing the necessary plasticizability of the mixture are
often chosen. These include, for example, cellulose-like
substances, polyethers, polyethylene glycol and others, which may
under some circumstances also act as pore formers when the
substances are removed wholly or partly by a thermal treatment
which generally follows the shaping operation. In the case of
pelletization in a corresponding pan pelletizer, the buildup
agglomeration is achieved by the gradual addition of a suitable
amount of water.
[0077] The thermal treatment is conducted in one step or in
sequential steps. Water components or else organic components are
removed here, and the mechanical strength of the shaped body is
generally increased in the process. In addition, the necessary
oxide phases are formed if the precursor materials were not yet in
this form.
[0078] In another mode of preparation, nitrate salts are used in
aqueous solution or the oxidic compounds are fully or partly
dissolved with nitric acid. Especially in the case of the aluminium
oxide-type compounds, complete dissolution is often not effected;
instead, the material is modified with the aid of the acid, this
operation being referred to as peptization. The peptide is then
mixed with the other dissolved components as described above and
processed to a shaped body. The effect of heat treatment is that
the respective oxides can form from the nitrates if the temperature
has been suitably chosen.
[0079] Another effect of the use of nitrate-containing salt
solutions may be that a precipitation reaction has to be conducted
in order to arrive at a solids mixture. The pH is adjusted with
sodium hydroxide or sodium carbonate solutions. Examples thereof
can be found in U.S. Pat. No. 4,535,071.
[0080] In addition, it is possible to convert nitrate salt
solutions to an oxidic product mixture in solid form by means of
spray drying. In general, there then follow a grinding operation
and a shaping operation as described above. A final heat treatment,
which can also be conducted directly after the spray drying or the
grinding of the constituents, brings about the necessary residual
nitrate breakdown and converts the components to the oxides and
consolidates the shaped body.
[0081] The above-described special production of the sorbent can be
dispensed with through use of a commercially available methanol
catalyst. Suitable examples are MegaMax.RTM. 700 and 800 from
Clariant (formerly Sud-Chemie) and Haldor Topsoe's Mk-101 and
Mk-121. These catalysts are described in Nitrogen+Syngas 290,
November-December 2007, page 36.
[0082] In contrast to the methanol synthesis, the purifying process
according to the invention is conducted in the absence of hydrogen.
100% absence of hydrogen can of course not be ensured in industry.
The "absence of hydrogen" should therefore be understood to mean a
hydrogen content of less than 1 ppm by weight, based on the total
mass of the contaminated hydrocarbon mixture.
[0083] The sorbent is preferably deposited as a purifying bed
directly upstream of the catalyst to be protected. It may be
present in the same vessel as the catalyst to be protected (i.e.
within the reactor) or in a vessel separately arranged upstream
thereof. The arrangement of the purifying bed within the reactor is
possible because no heat of reaction need be removed from or
supplied to the sorbent. According to the circumstances, residence
times between 0.01 and 0.2 hour are typically envisaged in the
purifying bed, but if required also higher. Since operation at
elevated temperature accelerates the depletion and increases the
sulphur capacity, it is advantageous to arrange it downstream of
the preheaters that are usually present. Observing a particular
temperature of the sorbent is crucial to its purifying capacity.
Experiments show that the contact should therefore take place at
temperatures between 10.degree. C. and 150.degree. C., preferably
between 20.degree. C. and 130.degree. C. and most preferably
between 30.degree. C. and 120.degree. C. The optimal contact
temperature is about 80.degree. C. Since commercial methanol
catalysts are used at much higher temperatures, thermal stability
exists within these ranges. If the catalyst to be protected is
operated at a different temperature, the sorbent should be disposed
in a separate vessel, i.e. outside the reactor.
[0084] What is important is that the contaminated hydrocarbon
mixture is exclusively in the liquid state during contact with the
sorbent. Within the specified temperature range, this is assured by
a pressure between 0.5 and 3.5 MPa (5 to 35 bar). However, the
pressure is ultimately unimportant, provided that the hydrocarbons
are in the liquid state. The weight hourly space velocity (WHSV) is
then preferably selected between 0.5 and 7 h.sup.-1. This means
that between 0.5 and 7 kilograms per hour of contaminated
hydrocarbon mixture are run through the purifying bed per kilogram
of sorbent. The purifying bed consists of a bed of the sorbent
having a bulk density in the range from 0.7 to 1.5 kg/m.sup.3,
preferably about 1.15 kg/m.sup.3.
[0085] The sorbent is typically supplied in an oxidized state,
which permits handling at room temperature under air. After the
reactors have been filled, there is no need to activate the
sorbents by a post-reduction. Even after use, the sorbents need not
be stabilized by oxidation with air, and so they can be removed
from the reactor in a simple manner.
[0086] In order to achieve particularly effective purification and
to avoid interruptions to operation resulting from exchange of the
sorbent, it is advisable to use a plurality of vessels which can be
connected in series in a revolving manner such that the vessel
having the highest loading is always disposed at the inlet and that
with the lowest loading at the outlet. In this case, without
interrupting the stream to be purified, at least one vessel can be
taken out and the material present therein can be rinsed and
removed, followed by refilling in an analogous manner.
[0087] The use of material having a high copper oxide surface area
is advantageous because the reaction rate of the adsorption and of
the conversion correlates therewith, and these materials also have
a higher sorption capacity. Preferably, the sorbent has a copper
oxide surface area of at least 50 m.sup.2/g, preferably 100
m.sup.2/g, based on the copper oxide content thereof. This promotes
the sorptive action. The surface area is determined by nitrogen
sorption.
[0088] What is important in the context of the present invention is
that the sorbent has essentially no catalytic activity in respect
of hydrogenation, etherification, oligomerization or further
reactions of olefins. These reactions of hydrocarbons are to
proceed exclusively over the catalysts intended therefor, and not
in the purifying bed. The catalysts to be protected are thus
outside the purifying bed, at least in another bed or in other
apparatuses.
[0089] The process according to the invention is suitable in
principle for the purifying of all hydrocarbon mixtures, preferably
of those having three to eight carbon atoms. Hydrocarbon mixtures
of industrial relevance are regarded as being, for example,
propene, n-butenes, n-pentenes, hexenes, neohexene, etc., and the
saturated analogues thereof. Among these, propane/propene and the
butanes/butenes are absolutely the most important.
[0090] The inventive sorbent can be used particularly
advantageously for purification of typical C.sub.4 hydrocarbon
streams in a state of workup immediately prior to conversion of the
butenes present therein. The "contaminants" include, as well as the
sulphur-containing compounds, also bases such as amines or
nitriles, for example, although these are below the detection
limit.
[0091] The process is of particularly good applicability to such
mixtures, since it efficiently removes contaminants that act as
poisons to the heterogeneous aluminium-, silicon- or
nickel-containing oligomerization catalysts.
[0092] The impurities that are to be removed in accordance with the
invention from the contaminated hydrocarbon mixture are preferably
organic sulphur compounds that act as catalyst poison in the
subsequent workup of the hydrocarbon mixture. The organic sulphur
compounds that are harmful to catalysts and are present in the raw
material streams typically obtainable include especially: [0093] a)
thiols having the general formula R--SH [0094] b) disulphides
having the general formula R--S--S--R' [0095] c) sulphides having
the general formula R--S--R' and [0096] d) substituted or
unsubstituted sulphur-containing heterocycles, such as thiophenes
and/or thiolanes in particular.
[0097] In the above-specified structural formulae, R and R' may be
identical or different alkyl, aryl, cycloalkyl or alkenyl radicals,
where R and R' are especially methyl, ethyl, propyl, butyl, phenyl,
cyclohexyl or butenyl radicals.
[0098] The particular advantage of the sorption material used in
accordance with the invention is that it chemically adsorbs the
contaminants, especially by arresting thiols present as contaminant
at the surface of the sorbent. Any disulphides are converted to a
thiol over the sorbent and then arrested. Chemisorption results in
a particularly high level of purification, such that the
hydrocarbon mixture is freed virtually completely of thiols and
disulphides.
[0099] The chemisorption of the catalyst poisons is irreversible.
For this reason, the sorbent used in accordance with the invention
cannot be regenerated. This means that highly contaminated
hydrocarbon streams rapidly exhaust the sorbent, such that it has
to be exchanged. In the interests of economically viable operation
of the purifying process, the proportion by weight of the
contaminants in the contaminated hydrocarbon mixture, based on the
total weight thereof, should be less than 0.2% by weight. More
preferably, the contaminated hydrocarbon mixture contains less than
100 ppm by weight and more preferably less than 10 ppm by weight of
impurities, in each case calculated as sulphur. In the case of such
a low level of contamination, the sorbent can be operated for a
very long period and additionally enables virtually complete
removal of the catalyst poisons.
[0100] The typical raw material mixtures originating from mineral
oil refineries have sulphur contents well above 0.2% by weight. For
this reason, it is necessary to prepurify the raw material mixture
in a prepurification stage upstream of the sorptive purification.
In the prepurification stage, the more highly contaminated raw
material mixture is prepurified to obtain a hydrocarbon mixture
having a contamination level below 0.2% by weight.
[0101] A suitable prepurification stage is especially the
above-described MEROX.RTM. scrub or a thioetherification, as
disclosed in DE102012212317A1, which was yet to be published at the
priority date of the present application.
[0102] The inventive form of purification is especially suitable
for being inserted into the flow as a safety net filter beyond a
MEROX.RTM. scrub.
[0103] In this context, a safety net filter is understood to mean a
second purifying instance which is arranged beyond a first
purifying instance and which has the function of conclusively
keeping residual amounts of the catalyst poisons that have not been
captured by the first purifying instance away from downstream
reaction steps or, in the case of disrupted operation in the first
instance, of ruling out immediate damage to the downstream reaction
steps.
[0104] Preferably, a MEROX.RTM. scrub serves as the first purifying
instance, which separates out most of the catalyst poisons in
relatively large amounts in advance. Only the mercaptans and
disulphides that are not captured by the MEROX.RTM. scrub are then
retained in the sorption bed in accordance with the invention. In
the case of disrupted operation in the MEROX.RTM. plant, the
sorbent takes on the full purifying function thereof and protects
the oligomerization from immediate irreversible damage. Since the
safety net filter in the normal state of operation takes on only a
small amount of adsorbate, it can be designed such that it has a
much smaller capacity than a MEROX.RTM. scrub. This corresponds to
the speed at which it is exhausted in the event of a fault. The
suitable dimensions of the safety net filter depend on how quickly
the incoming mixture can be diverted.
[0105] Thioethers, being comparatively unreactive substances, are
barely removed in MEROX.RTM. scrubs. In order to avoid excessively
large concentrations on entry into the sorption bed, they are
preferably removed in a distillation as high boilers at a suitable
point in the process procedure upstream of the sorption bed.
[0106] In combination with a prepurification stage such as a
MEROX.RTM. scrub, the sorbent described here can be used
irreversibly without hesitation. An irreversible use in this
context is understood to mean that no direct regeneration, i.e.
recovery of the active sorbent, is effected as soon as it is
deactivated. This does not rule out recycling of the spent sorbent
by recovering the metals present therein, such as the copper in
particular, by metallurgical means. This is because, in such a
metallurgical treatment, the original composition of the sorbent is
lost, and so it is not possible to speak of a regeneration in this
context.
[0107] The process according to the invention is basically suitable
for desulphurization of hydrocarbon streams having three to eight
carbon atoms. However, it is used with particular preference for
removing poisons from C.sub.4 streams that are obtained as crack C4
or as FCC C4 or the corresponding raffinates thereof in the
refining of mineral oil. Thus, the contaminated hydrocarbon mixture
preferably fulfils one of the following specifications A, B, C and
D, each of which adds up to 100% by weight, the stated proportions
by weight each being based on the total weight of the contaminated
hydrocarbon mixture:
Specification A:
[0108] isobutane 20% to 40% by weight, preferably 30% to 37% by
weight; [0109] n-butane 5% to 18% by weight, preferably 8% to 10%
by weight; [0110] 1-butene 5% to 15% by weight, preferably 12% to
14% by weight; [0111] isobutene 12% to 25% by weight, preferably
15% to 20% by weight; [0112] 2-butenes 9% to 40% by weight,
preferably 20% to 30% by weight; [0113] 1,3-butadiene 0% to 3% by
weight, preferably 0.5% to 0.8% by weight; [0114] water 0% to 1% by
weight, preferably less than 0.1% by weight; [0115] contaminants,
especially sulphur-containing hydrocarbons, less than 0.5% by
weight, preferably less than 0.2% by weight;
Specification B:
[0115] [0116] isobutane 0.6% to 8% by weight, preferably 1% to 7%
by weight; [0117] n-butane 0.5% to 8% by weight, preferably 4% to
7% by weight; [0118] 1-butene 9% to 25% by weight, preferably 10%
to 20% by weight; [0119] isobutene 10% to 35% by weight, preferably
20% to 30% by weight; [0120] 2-butenes 3% to 15% by weight,
preferably 5% to 10% by weight; [0121] 1,3-butadiene 25% to 70% by
weight, preferably 40% to 50% by weight; [0122] water 0% to 1% by
weight, preferably less than 0.5% by weight; [0123] contaminants,
especially sulphur-containing hydrocarbons, less than 0.5% by
weight, preferably less than 0.2% by weight;
Specification C:
[0123] [0124] isobutane 0.6% to 8% by weight, preferably 1% to 7%
by weight; [0125] n-butane 0.5% to 15% by weight, preferably 4% to
13% by weight; [0126] 1-butene 9% to 40% by weight, preferably 10%
to 35% by weight; [0127] isobutene 10% to 55% by weight, preferably
20% to 50% by weight; [0128] 2-butenes 3% to 25% by weight,
preferably 5% to 20% by weight; [0129] 1,3-butadiene 0% to 1% by
weight, preferably less than 0.8% by weight; [0130] water 0% to 1%
by weight, preferably less than 0.5% by weight; [0131]
contaminants, especially sulphur-containing hydrocarbons, less than
0.5% by weight, preferably less than 0.2% by weight;
Specification D:
[0131] [0132] n-butane 10% to 30% by weight, preferably 25% to 30%
by weight; [0133] 1-butene 0.2% to 45% by weight, preferably 5% to
30% by weight; [0134] 2-butenes 35% to 85% by weight, preferably
50% to 75% by weight; [0135] water 0% to 1% by weight, preferably
less than 0.1% by weight; [0136] contaminants, especially
sulphur-containing hydrocarbons, less than 0.5% by weight,
preferably less than 0.1% by weight.
[0137] Specification A describes typical FCC C4, while
specification B describes typical crack C4. Specification C
describes a typical raffinate I from crack C4. Specification D
describes a raffinate III from FCC or CC4.
[0138] After the contaminated hydrocarbon mixture has been freed of
its catalyst poisons in accordance with the invention, the
customary workup of such mixtures can be effected, without any risk
of poisoning the catalysts used downstream. The typical workup
steps that may follow the purification described here include:
[0139] a) extraction of 1,3-butadiene present in the hydrocarbon
mixture; [0140] b) selective hydrogenation of diolefins and/or
acetylenes present in the hydrocarbon mixture to olefins; [0141] c)
oligomerization of olefins present in the hydrocarbon mixture to
corresponding oligomers; [0142] d) distillative removal of 1-butene
and/or isobutane present in the hydrocarbon mixture, especially
with the purpose of obtaining 1-butene and/or isobutane in high
purity; [0143] e) removal of isobutene present in the hydrocarbon
mixture by conversion of the isobutene with water to tert-butanol
and/or with methanol to methyl tert-butyl ether; [0144] f)
dehydrogenation of butanes present in the hydrocarbon mixture to
butenes; [0145] g) oxidative dehydrogenation of butenes present in
the hydrocarbon mixture to butadiene; [0146] h) alkylation of
n-butene present in the hydrocarbon mixture with isobutane likewise
present; [0147] i) oxidation of hydrocarbons having four carbon
atoms present in the hydrocarbon mixture for preparation of maleic
anhydride.
[0148] It will be appreciated that not all the workup steps a) to
i) enumerated need be conducted; it is also possible to conduct
only individual workup steps. The sequence enumerated is not
binding either.
[0149] Furthermore, individual workup steps among those enumerated
may also be arranged upstream of the inventive purification,
provided that they are not sensitive to the catalyst poisons. At
least a nickel-catalysed oligomerization should be protected by the
inventive sorbent, since organic sulphur compounds, even in very
small concentrations, poison nickel catalysts.
[0150] If the hydrocarbon mixture used is also contaminated with
water, it is advisable to free the water-contaminated hydrocarbon
mixture of water before entry into the purifying bed, i.e. to dry
it. The motivation for removing the water is as follows: Since
homogeneously dissolved water in the mixture somewhat attenuates
the action of the sorbent, the stream is preferably dried before
entry into the purifying bed, for example by means of an azeotropic
distillation (drying distillation).
[0151] The basic structure of such value addition chains
incorporating the inventive removal of poisons are to be
illustrated in detail hereinafter. The figures show, in schematic
form:
[0152] FIG. 1: C.sub.4 line with coarse and fine desulphurization
at the start;
[0153] FIG. 2: C.sub.4 line with sorptive purification immediately
upstream of the oligomerization.
[0154] FIG. 1 shows, in schematic form, a line for workup of
C.sub.4 hydrocarbon mixtures.
[0155] A raw material source 0 supplies a raw material mixture 1
comprising predominantly hydrocarbons having four carbon atoms
(butenes and butanes). The raw material source 0 may, for example,
be a mineral oil refinery. According to whether the cracker works
by fluid catalysis or is operated as a steamcracker, a resulting
raw material mixture 1 is referred to as FCC C4 or as crack C4.
[0156] Alternative raw material sources 0 or raw material mixtures
1 also include DCC C4 (DCC: "Deep catalytic cracking"), pyrolysis
C4, C4 from MTO ("methanol-to-olefins") or MTP
("methanol-to-propylene") processes or C.sub.4 from
dehydrogenations of n-butane.
[0157] Since raw C.sub.4 streams may have a high sulphur content
depending on their source 0, the raw material mixture 1 is first
coarsely prepurified in a prepurification stage 2, by removing
sulphur-containing constituents 3 in relatively large amounts. The
pre-purification stage 2 may, for example, be a MEROX.RTM. scrub or
a thioetherification. Alternatively, it is also possible here to
use a reversible sorbent which is regenerated cyclically. However,
since the separation performance of a MEROX.RTM. scrub or a
thioetherification is much greater, these prepurification stages
are preferable over a sorptive coarse purification.
[0158] A hydrocarbon mixture 4 which is then drawn off from the
prepurification stage 2 is still contaminated (contamination level
max. 0.2% by weight, preferably below 100 ppm by weight). The
contaminated hydrocarbon mixture 4, for complete elimination of the
catalyst poisons present therein, is run into a purifying bed 5.
The purifying bed 5 is a bed of a solid comprising copper oxide,
zinc oxide and aluminium oxide, the sorbent. The purifying bed 5 is
present in a vessel known per se. The liquid, contaminated
hydrocarbon mixture 4 flows through the vessel, such that the
sorbent present therein chemically adsorbs the contaminants present
in the hydrocarbon mixture 4 and hence arrests them in the
purifying bed 5. In this way, a purified hydrocarbon mixture 6 is
obtained, which has been virtually completely freed of catalyst
poisons.
[0159] In accordance with its material of value composition, a
workup known per se is then effected on the materials of value
present in the raw material mixture 1. If the raw material mixture
1 is crack C4, it has a high content of butadiene 7, which is
removed by extraction in a butadiene removal 8.
[0160] Residues of unextracted butadiene are selectively
hydrogenated (not shown). This gives what is called "raffinate I"
9.
[0161] The isobutene 10 present in the raffinate I is removed in an
isobutene removal 11. The isobutene removal 10 generally involves
an MTBE synthesis in which the isobutene is reacted with methanol
to give methyl tert-butyl ether (MTBE) and a downstream MTBE
cleavage in which the MTBE is cleaved back to isobutene 10.
[0162] The mixture which has been freed of isobutene is referred to
as "raffinate II" 12. The material of value present therein,
1-butene 13, is distilled off in a 1-butene removal 14. This gives
what is called "raffinate III" 15.
[0163] Raffinate III 15 contains, as material of value, essentially
only the two 2-butenes, which are converted in an oligomerization
16 to C.sub.8 olefins. The oligomerizate 17 is separated by
distillation and subsequently processed by hydroformylation and
hydrogenation to give plasticizer alcohols (not shown).
[0164] FIG. 2 shows one variant of a C.sub.4 line in which the
purifying bed 5 is arranged immediately upstream of the
oligomerization 17. This is an option especially when a
thioetherification which works in the presence of hydrogen is used
as prepurification stage 2. Some of the hydrogen is also required
beyond the butadiene removal 8, in order to selectively hydrogenate
butadiene that has not been removed. Since the hydrogen is
discharged from the C.sub.4 line at a stage no later than the
isobutene removal 11 or the 1-butene removal 14, the fine
desulphurication then takes place in the purifying bed 5 in the
absence of hydrogen.
[0165] Alternatively, the purifying bed 5 could also be charged
with raffinate I 9. In that case, it would be arranged beyond the
butadiene removal 8 and upstream of the isobutene removal 11 (not
shown). This is advantageous especially when the raw material
mixture 1 used is crack C4 containing large amounts of
1,3-butadiene according to specification B. 1,3-Butadiene could
deactivate the sorbent too quickly. The purifying bed should
therefore if at all possible be charged with a butadiene-depleted
hydrocarbon mixture, i.e. at least with raffinate I or with FCC
C4.
EXAMPLES
First Experiment
Removal of Ethanethiol According to the Invention
[0166] The sorbent used is a solid purchased from Clariant AG,
which is usable as methanol catalyst. The sorbent contains about
42% by weight of CuO, about 44% by weight of ZnO, about 12% by
weight of Al.sub.2O.sub.3 and about 2% by weight of graphite, and
is in the form of tablets (5.times.3 mm). The specific copper oxide
surface area, measured by means of nitrogen sorption, is 100
m.sup.2 per g of copper oxide content.
[0167] 120 g of sorbent are introduced into each of two reaction
tubes having diameter 1 cm. The bulk density is about 1.2
kg/dm.sup.3. The filled tubes are connected in series, with one
sampling valve mounted between the tubes (discharge 1) and one at
the end (discharge 2). The purifying beds are brought to a
temperature of 80.degree. C. by heating the tube walls, and a
liquid mixture containing about 33% by weight of 1-butene, about
23% by weight of trans-2-butene, about 15% by weight of
cis-2-butene and about 27% by weight of n-butane is allowed to flow
through them at a pressure of 24 bar. As a contaminant, the
material contains an average of 5.4 mg/kg of sulphur, predominantly
in the form of ethanethiol. The loading of the purifying beds is
600 g/h, and so the sulphur input is about 3.2 mg/h.
[0168] As shown by the analyses, the sulphur is at first already
removed virtually quantitatively from the mixture in the first
purifying bed. From an operating time of 480 hours onward, the
sulphur content at discharge 1 rises rapidly. This sharp
breakthrough corresponds to an arrested amount of sulphur of about
1.7 g or a sulphur absorption in the purifying bed of about 1.4% by
weight. The breakthrough downstream of the second purifying bed
(discharge 2) takes place at about 1200 hours. At this time, the
purifying beds have absorbed a total of about 3.9 g of sulphur,
corresponding to a mean absorption of 1.7% by weight, based on the
freshly introduced sorbent.
[0169] The discharge values of the individual C.sub.4 components
remained unchanged compared to the corresponding feed values over
the entire experimental period.
[0170] After the end of this experiment, the beds are purged with
nitrogen. The sorbent can be removed intact and with sufficient
stability.
[0171] The results of the experiment are recorded in Table 1.
TABLE-US-00002 TABLE 1 Results from experiment 1 Mean S Mean
decrease in content [% by S [% by wt.] Mean S content wt.] in Mean
S content [% in discharge [% by wt.] discharge by wt.] in discharge
2 compared to in feed 1 up to 480 h 2 up to 1200 h feed up to 1200
h 0.00054 0.00003 0.00002 96
Second Experiment
Removal of Methanethiol According to the Invention
[0172] The sorbent used and the experimental setup correspond to
the first experiment.
[0173] Analogously to experiment 1, 5 mg/kg of sulphur are supplied
as impurity, predominantly in the form of methanethiol. The loading
of the two purifying beds, each of which has been charged with 28
g, is 380 g/h, i.e. the sulphur input is 1.9 mg/h. The contact
temperature was set to 100.degree. C.
[0174] As shown by the analyses, the sulphur is at first already
removed virtually quantitatively from the mixture in the first
purifying bed. From an operating time of about 410 hours onward,
the sulphur content at discharge 1 rises. This sharp breakthrough
corresponds to an arrested amount of sulphur of about 0.5 g or a
sulphur absorption by the sorbent of about 1.9% by weight. The
breakthrough downstream of the second purifying bed (discharge 2)
takes place at about 720 hours. At this time, the purifying beds
have absorbed a total of about 1.9 g of sulphur, corresponding to a
mean absorption of 1.7% by weight, based on the freshly introduced
sorbent.
[0175] The discharge values of the individual C.sub.4 components
remained unchanged compared to the corresponding feed values over
the entire experimental period.
[0176] After the end of this experiment, the beds are purged with
nitrogen. The sorbent can be removed intact and with sufficient
stability.
[0177] The experimental results are shown in Table 2.
TABLE-US-00003 TABLE 2 Results from experiment 2 Mean S content [%
by Mean S Mean wt.] in content [% by Mean decrease in S [% S
content discharge wt.] in by wt.] in discharge 2 [% by 1 up to
discharge 2 up to compared to feed up to wt.] in feed 410 h 720 h
720 h 0.00044 0.00004 0.00004 91
Third Experiment
Removal of Diethyl Disulphide According to the Invention
[0178] The sorbent used and the experimental setup correspond to
the first and second experiments.
[0179] Analogously to experiment 1, 1 mg/kg of sulphur are supplied
as impurity, predominantly in the form of diethyl disulphide. The
loading of the purifying beds, each of which contains 28 g of the
sorbent, is 360 g/h, and so the sulphur input is about 0.4 mg/h.
The operating temperature is 100.degree. C.
[0180] As shown by the analyses, the sulphur is at first already
removed virtually quantitatively from the mixture in the first
purifying bed. From an operating time of 600 hours onward, the
sulphur content at discharge 1 rises rapidly. This sharp
breakthrough corresponds to an arrested amount of sulphur of about
0.3 g or a sulphur absorption by the sorbent of about 1.2% by
weight. The breakthrough downstream of the second purifying bed
(discharge 2) takes place at about 1080 hours. At this time, the
purifying beds have absorbed a total of about 0.6 g of sulphur,
corresponding to a mean absorption of 1.2% by weight, based on the
freshly introduced sorbent.
[0181] The discharge values of the individual C.sub.4 components
remained unchanged compared to the corresponding feed values over
the entire experimental period.
[0182] After the end of this experiment, the beds are purged with
nitrogen. The sorbent can be removed intact and with sufficient
stability.
[0183] The experimental results are shown in Table 3.
TABLE-US-00004 TABLE 3 Results from experiment 3 Mean S content [%
by Mean S wt.] in content [% by Mean decrease in S [% Mean S
discharge 1 wt.] in by wt.] in discharge 2 [% by up to discharge 2
up to compared to feed up to wt.] in feed 600 h 1080 h 1080 h
0.00010 0.00001 0.00001 90
Fourth Experiment
Removal of Dimethyl Disulphide with the Aid of Zeolites (not
Inventive)
[0184] A sorbent is produced according to EP0354316. It is based on
a type X zeolite and contains only 10% by weight of Cu. The two
tubes, each charged with 50 g of the material, are connected in
series, with one sampling valve mounted between the purifying beds
(discharge 1) and one at the end (discharge 2). The beds are
brought to a temperature of 120.degree. C. by heating the tube
walls, and a liquid mixture containing about 33% by weight of
1-butene, about 23% by weight of trans-2-butene, about 15% by
weight of cis-2-butene and about 27% by weight of n-butane is
allowed to flow through them at a pressure of 30 bar. As a
contaminant, the material contains an average of 2.0 mg/kg of
sulphur, predominantly in the form of dimethyl disulphide. The
loading of the purifying beds is 375 g/h, and so the sulphur input
is about 0.75 mg/h.
[0185] As shown by the analyses, the sulphur is at first already
removed virtually quantitatively from the mixture in the first
reactor. From an operating time of 48 hours onward, however, the
sulphur content at discharge 1 rises rapidly. This sharp
breakthrough corresponds to an adsorbed amount of sulphur of only
about 0.036 g or a sulphur absorption by the sorbent of about
0.036% by weight. The breakthrough downstream of the second
purifying bed (discharge 2) takes place at about 96 hours. At this
time, the purifying beds have absorbed a total of about 0.07 g of
sulphur, corresponding to a mean absorption of 0.07% by weight,
based on the freshly introduced sorbent.
[0186] With the noninventive material, distinct desulphurization
can accordingly be achieved only for a very short time, and the
material used is not in any relation to the purifying
performance.
[0187] The results are shown in Table 4.
TABLE-US-00005 TABLE 4 Results from experiment 4 Mean decrease Mean
S in S [% by wt.] content Mean S content [% Mean S content [% in
discharge [% by by wt.] in discharge by wt.] in discharge 2
compared to wt.] in feed 1 up to 48 h 2 up to 96 h feed up to 96 h
0.00020 0.000005 0.000005 97
CONCLUSION
[0188] The experiments demonstrate that the sorbent used in
accordance with the invention has the following properties: [0189]
it binds the sulphur from sulphur compounds virtually completely;
[0190] it does not require any activation in the hydrogen stream,
nor any other additional operating materials; [0191] it does not
require any periodic purifying and desorption streams, since it is
an irreversible sorbent; [0192] it can be accommodated in a simple
vessel through which the mixture simply flows, preferably at
slightly elevated temperature, as is typically often necessary in
any case for the feeding of downstream reactors; [0193] it causes
virtually no side reactions of olefins, such as oligomerization,
isomerization and hydrogenation, and hence also no losses; [0194]
it does not release any substances whatsoever in concentrations
that have any influence at all on the downstream processing stages;
[0195] in view of the long lifetime at typical sulphur
concentrations below 5 ppmw and a capacity of at least 1% by weight
of sulphur, it is very inexpensive to operate, even though it
cannot be regenerated directly, and can instead only be sent to a
raw material utilization after the capacity has been exhausted;
[0196] it can be handled and disposed of without any problem, since
it is neither classified as carcinogenic nor exhibits pyrophoric
properties.
LIST OF REFERENCE NUMERALS
[0196] [0197] 0 raw material source [0198] 1 raw material mixture
[0199] 2 prepurification stage [0200] 3 sulphur-containing
constituents [0201] 4 contaminated hydrocarbon mixture [0202] 5
purifying bed [0203] 6 purified hydrocarbon mixture [0204] 7
butadiene [0205] 8 butadiene removal [0206] 9 raffinate I [0207] 10
isobutene [0208] 11 isobutene removal (MTBE synthesis/MTBE
cleavage) [0209] 12 raffinate II [0210] 13 1-butene [0211] 14
1-butene removal [0212] 15 raffinate III [0213] 16 oligomerization
[0214] 17 oligomerizate
* * * * *